Moon Cozies Up to Jupiter in the Night Sky Sunday

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For the second time this month, the moon is going to pay a visit
to Jupiter, the largest planet in our solar system.

On Sunday and Monday evenings (Jan. 29 and 30), a fat,
waxing crescent moon will appear to
slide past the planet Jupiter. Of course, the moon is much
closer to Earth than Jupiter and as such, can change its position
against the background stars rather quickly.

In fact, relative to the background stars, the moon will appear
to move east at roughly its own apparent width each hour – or
about 12 degrees (on average) over a span of 24 hours.
The sky
map of Jupiter and the moon with this story shows how
they will appear together at about 9 p.m. local time to observers
in mid-northern latitudes.

On Sunday evening, look for Jupiter hovering about 7 degrees to
the upper left of the moon; on Monday evening, however, you'll
note that the moon will be a similar distance from Jupiter, but
will have shifted almost directly above it. As a benchmark, 10
degrees could be visualized as roughly the equivalent of your
clenched fist held at arm's length. [ Skywatcher
Photos: Jupiter & the Moon ]

Jupiter is perched at Venus' upper left during the early evening
hours. The "King of the Planets" shines brightly enough —
two-and-a-half times brighter than Sirius, the brightest star
(itself located at dusk shining brilliantly low in the southeast
sky).

And yet, Venus is still nearly five times brighter than Jupiter.
The two planets will be slowly edging closer together in the
coming weeks. They'll appear closest to one another, just 3
degrees apart, Mar. 13.

This week, Jupiter doesn't set until around midnight local time,
which means it's still high enough at nightfall for steady images
in a telescope; Jupiter is enveloped like Venus in a perpetual
cloud cover. Broad cloud bands cross the planet and are
visible even in a small telescope, appearing to cross its disk
parallel to the planet's equator.

Jupiter's disk is noticeably flattened at its poles because the
giant planet is turning so fast on its axis — once around every 9
hours 50 minutes. For comparison, if Earth rotated on its axis as
fast as Jupiter, our day would be only 53 minutes long!

A small telescope should also reveal
four of Jupiter's moons — the famous "Galilean Satellites"
that were discovered by Galileo with his crude telescope in
January 1610.

It's always interesting to watch these four moons through a
telescope as they appear to change their positions relative to
each other from hour to hour and from night to night.

On Sunday night, for instance, if you train a telescope on
Jupiter — or even steadily hold binoculars with at least 7-power
magnification — you'll see two moons, Ganymede and Callisto, on
one side of Jupiter, while the other two, Io and Europa, will be
on the other side. But on Monday evening, three moons will be
gathered on one side (Ganymede, Io and Europa) while Callisto
sits by itself on the other side of the big planet.

Editor's note: If you snap an amazing photo of Jupiter and the
moon, or any other skywatching target, and would like to share it
with SPACE.com, contact managing editor Tariq Malik
at tmalik@space.com.

Joe Rao serves as an instructor and guest lecturer at New
York's Hayden Planetarium. He writes about astronomy for The New
York Times and other publications, and he is also an on-camera
meteorologist for News 12 Westchester, New York.